Load bearing pivots for balances and compensating means therefor



W. STELZER March 27, 1956 LOAD BEARING PIVOTS FOR BALANCES ANDCOMPENSATING MEANS THEREFOR Filed Oct. 26, 1955 I 1 JNVENYQOR. Maw WUnited States Patent LOAD BEARING PIVOTS FOR BALANCES AND COMPENSATIN GMEANS THEREFOR William Stelzer, Summit, N. J. Application October 26,1953, Serial No. 388,173

8 Claims. (Cl. 265-63) The invention relates to Weighing mechanisms andmore particularly to spring type load bearing pivots for balances andcompensating means therefor. This application is a continuation-in-partof my application Ser. No. 180,620 filed Aug. 21, 1950, now Patent No.2,681,222.

Spring type pivots consisting of plates or short leaf springs have beensuccessfully used to eliminate friction in balances where the loadcarrying beam travels only a short distance. While such leaf springpivots are very practical they nevertheless have the disadvantage thatthe effective pivot point is not fixed while the leaf spring fiexes,aiiecting the accuracy of the balance because the lengths of the leveror links change.

The object of the present invention is to provide a novel torsionalpivot of rugged construction where the pivotal axis remains fixed.

Another object is to provide a pivot pin acting as a spring offering aminimum resistance to torsion but maximum resistance to bending.

A further object of the invention is to incorporate means to compensatefor the varying torsional resistance of the pivot pin to control thesensitivity of the balance.

Other objects and advantages of this invention will be apparent from thefollowing detailed description considered in connection with theaccompanying drawing submitted for the purpose of illustration and notto define the scope of the invention, reference being had for thatpurpose to the subjoined claims. In the drawing, wherein similarreference characters refer to similar parts throughout the severalviews:

Fig. l is a front view of a conventional counterscale or comparingbalance using pivots of the improved design;

Fig. 2, a sectional front elevation of a weigher incorporating myinvention;

Fig. 3, a section taken on lines 3-3 of Fig. 2;

Fig. 4, an enlarged end view of the novel torsional pivot pin;

Fig. 5, a side view thereof;

Fig. 6, a detail view of a bracket for supporting a pivot pin, the viewbeing in the same direction as in Fig. 2;

Fig. 7, a fragmentary view on a larger scale of the beam of the weigherincorporating a modified pivot pin, looking in the direction of Fig. 2;

Fig. 8, a section taken on lines 8-8 of Fig. 7;

Fig. 9, a section taken on lines 99 of Fig. 8;

Fig. 10, an elevation of a leaf spring making up the modified pivot pin;

Fig. 11, a plan view of another leaf spring of the modified pivot pin;

Fig. 12, a section showing the invention incorporated in a cantilevertype pivot pin as applied to a balance illustrated in Fig. l; and

Fig. 13, a section taken on lines 13-13 of Fig. 12 with the beamremoved.

Before explaining the present invention in detail, it is to beunderstood that the invention is not limited in its application to thedetails of construction and arrangement of parts illustrated in theaccompanying drawing, since the invention is capable of otherembodiments and of being practised or carried out in various ways. Alsoit is to be understood that the phraseology or terminology employedherein is for the purpose of description and not limitation.

The invention is shown incorporated in a weighing echanism of a classdisclosed in the above-mentioned co-pending application, but it isapparent that the pivot and compensating device can be used equaly wellin conventional balances. Such a balance is illustrated in Fig. l, wherenumeral 1 indicates a frame or base supporting a pair of parallel beams2 by fulcrums 3, the beams carrying a pair of vertical bars 4 providedwith platters or pans. The bars are connected by pivots 5 which are at ahigher elevation than fulcrum 3 to give a compensating effect as theresultant force of both bars acts above fulcrum 3. Fulcrurns 3 as wellas pivots 5 may contain the novel pivots described in detail later withreference to Figs. 44.3. Referring now to Figs. 2 and 3, the weighingmechanism comprises a base 11 within which is housed a beam indicated inits entirety by numeral 12 and pivotally supported by base 11 at fulcrum13 through the medium of an inverted U-shaped bracket 14 secured to base11 with screws 15. Beam 12 has an arm 16 supporting a resistantconsisting of a Weight 17 provided with an adjusting screw 18 foradjusting the center of gravity of weight 17 vertically and andadjusting screw 19 for adjusting the force of the resistant. An oppositehorizontal arm 20 of beam 12 has a pivot 13' to pivotally support a loadcarrying member 22 through the medium of another inverted U-shapedbracket 14 similar to bracket 14. The load carrying member 22 consistsof an upright post whose upper end carries a rigidly secured platter 23on which the load to be weighed is placed. A fixed upright post 24secured at it lower end to base 11 by screws 15 serves to support at itsupper extremity one end of a horizontal leaf spring 25 whose other endis clamped between load carrying member 22 and platter 23, this leafspring 25 and arm 20 serving as parallel arms to restrict load carryingmember 22 to a vertical movement where all points of platter 23 haveequal velocity. The lower fixed end of post 24 is extended at 26 torestrict the vertical movement of load carrying member 22. The latterhas racks 27 carrying complemental weights 28 of known weight which maybe shifted to stationary racks 29 extending horizontally from post 24.

The complemental weights serve to counterbalance weight 17 so that beam12 is in equilibrium. When a load to be weighed is placed on platter 23,the weights removed from rack 27 until equilibrium is attained are equalto the weight of the load.

The pivots 13 and 13' comprise pivot pins 31 of spring steel or otherresilient material pressed into bores in bosses 32 of beam 12 so thatthe pressed-in part cannot turn. The ends of the pins have shoulders 33as shown in Figs. 4 and 5, fitting tightly into the square holes 34(Fig. 6) of brackets 14 and 14 so that the ends are firmly held againstrotation. Fig. 3 illustrates that pins 31 extend equal distances fromboth sides of beam 12 and that twisting of the pin is restricted to theportion between hole 34 and the side of beam 12. In order to maketwisting possible, the pin is weakened against torsion and reinforcedagainst bending by being fluted or starshaped in cross-section, or thepin may be considered as having a plurality of radial fins or leaves 35being radially disposed from the axis of pin and extendinglongitudinally and parallel with the axis of the pin. Each fin may beconsidered as a beam whose height increases the resistance to bending ofthe central axis and whose width is reduced to thereby decrease theresistance against greases torsion. It will be noted that twisting ofthe pin in no way changes the position of the pivot, because all finsare symmetrical about the central axis of pin 31, whereby the distancebetween pivots 13 and13 or between fulcrums 3 and pivots 5 remainsconstant at all times.

Pin 31 may be regarded as a torsion spring which offers a resistance totwisting, this resistance increasing proportionally with the rotarydistortion or twist. To compensate for such resistance the pivots may bepositioned as shown in Fig. l where the resultant center of gravity ofthe gravitational forces transmitted by bars 4 to beams 2 is located ashort distance above fulcrums 3, or in the construction shown in Fig. 2the center of gravity of weight 17 and of the weight acting on pivot 13are located a short distance above pivot or fulcrum 13, so that theresultant of the gravitational force of weight 17 and the gravitationalforce acting on fulcrum 13 is located a short distance vertically abovepivot 13. The latter distance may be changed by adjusting screw 18; thegreater the distance, the greater is the compensating force. Theresistance of pins 31 can also be compensated for by an over-centerspring such as by a helical compression spring 38 adjustably supportedat one end 40 by an adjusting screw 39 in base 11 and the other end 40engaging an extension 41 of beam 12, one portion of this extensionserving as an indicator or pointer 42. The ends 40 and 40 as well as thecentral straight wire 43 are concentric with the coils of the spring andfit snugly into respective holes in screw 39 and extension 41 so thatthere is no play but yet screw 39 may be turned. Spring 38 and extension41 together act as a toggle, where the coils near extension 41 are theknee, extension 41 and straight portion 43 are the legs of the togglepivoted at 13 and coils 44 respectively. A similar compensating springhas been shown in my co-pending application Ser. #345,813, filed Mar.31, 1953, now Patent No. 2,698,747. When the spring is on dead center,the adjusting force is zero, while movement away from dead centerincreases the moment about fulcrum 13 in one direction and decreases itin the other direction proportional to the movement so that theresistance of pin 31.

may be fully compensated.

In the modification shown in Figs. 7-11 the pivot pin is made up of twoseparate flat springs 50 and 51 assembled at right angles to each otheras shown in Fig. 9 to serve as the skeleton for a pin of rubber orrubberlike material 52. The rubber is moulded after springs 50 and 51are placed into the bores in bosses 32 so that the rubber is thoroughlybonded not only to the springs but also to lever 12. The central portion53 is cylindrical, but the ends 54 are square to firmly fit into squareholes 34 of brackets 14 and 14'. Rubber collars 55 are moulded tocylindrical portions 53 to rest against the inside surface of brackets14 and 14. If the rubber pin is to be moulded separate from beam 12 andafterwards pressed into the holes of bosses 32, then collars 55 shouldbe omitted. Spring 50 has longitudinal slots 56 restricted in width atstepped ends 57 to the thickness of the spring so that when assembledover ends 58 of spring 51 a solid construction is obtained that can bepressed into holes 34. Shoulders 59 rest against the inside surface ofthe downwardly pointing legs of brackets 14 and 14. Spring 51 has solidends but the intermediate portion is slotted at 60 with a narrower slot61 in the center so that the central portion of spring 50 fits into thisslot and serves to stiffen spring 51 against contraction towards theaxis of the pivot. The rubberlike material moulded in place not onlyserves to hold the assembly of springs and beam together, but also helpsto produce a better grip between beam and pin as well as between pin andbracket, as this is necessary to prevent any possible friction.

The pivot in Figs. 12 and 13 consists of a cantilever pin 65 ofresilient material as incorporated in a balance shown in Fig. 1. Thispin is cross shaped in cross-section as shown in Fig. 13 and has an endpressed into a hole in bearn'Z. The other end or shank 66 is leftcylindrical and is pressed tightly into support 1 or into verticalmember 4. A central hole 67 serves to further weaken the pin againsttorsion, as hole 67 extends through the free or unsupported portion ofthe pin to separate the fins or leaves 68 into four separate leafsprings radially disposed and extending longitudinally parallel with theaxis of pin 65. Hole 67 extends also through shank 66 merely because itis easiest to separate fins 68 by drilling a small hole prior to millingflutes which produce the fins 68. If the pin is moulded of a toughresilient plastic, shank 67 may be left solid.

Describing now the operation of the weigher shown in Figs. 2-6, thedevice is in balance when all weights are on pins 27 and no load is onplatter 23. If one weight is shifted onto fixed rack 29, then if a loadequal to the removed weight is placed on platter 23, the weigher is inbalance and the points of the racks lined up as shown. The torsionalresistance of pivot pins 13 and 13' causes a turning moment in beam 12which must be compensated by adjusting weight 17 or 19 to obtain abalanced position as shown, when the load carrying member 22 carries allweights and no load. A further com pensation is obtained by spring 33,which compensates for the rate of increase in the torsional resistanceof pivot pins 13 and 13'.

The weigher in Fig. 1 is in balance because it is symmetrical aboutfulcrums 3. The pivot pins are not under torsional stress when theweigher is in the position shown. The compensation for the torsionalresistance of the pivot pins in pivots 3 is provided by placing thecenter of gravity of the beams above the axes of the fulcrums. Thus theweight of a beam concentrated above its fulcrum compensates for thechange in resistance of the pivot pin. The distance of the center ofgravity of beam 2 above fulcrum 3 depends on the torsional stiffness ofthe pivot pin. If the torsional resistance is small, then the distanceof the center of gravity above fulcrum 3 can be short. In using theweigher the load is placed on the platter of one vertical bar 4 andknown weights on the other until the pointer is in the center. If thepointer is not vertical and the pins stressed to offer a resistance,then the center of gravity has moved over dead center whereby the weightconcentrated at the center of gravity produces a turning moment whichcompensates for the resistance of the pivot pins. In pin shown in Fig.12 torsion takes place only in the position intermediate frame 1 andbeam 2.

The pivot pin shown in Figs. 7-11 operates in a similar manner as pin31. The outer ends are rigidly supported and the central portion isfirmly secured to beam 12 so that twisting takes place only intermediatethe outer fixed ends and the portion fixed to beam 12.

Having thus described my invention, I claim:

1. In Weighing mechanisms including a member rotatable relative toanother member, in combination, a pivot element comprising a resilientstraight pin of symmetrical cross-section weakened to yield to torsionalstresses, means to reinforce said pin against bending of its axis, saidpin having a portion rigidly secured to one of said members and anotherportion rigidly secured to the other of said members, whereby saidmembers may be rotated relative to each other a short angular distanceabout said pin by torsion of said pin, said pin ofiering an increasingresistance proportional to the angular distortion of said pin, andcompensating means to compensate for the increase in resistance totorsion of said pin to render said resistance approximately constant.

2. In weighing mechanisms including a member rotatable relative toanother member, in combination, a torsional pivot element consisting ofleaf springs arranged to offer reduced resistance to torsional stressesbut increased resistance to bending stresses, said leaf springs having aportion rigidly secured to one of said members and another portionrigidly secured to the other of said members, whereby said members maybe rotated relative to each other a short angular distance about saidpivot element by torsion of said pivot element, and means to compensatefor the resistance to torsion offered by said leaf springs.

3. In a weighing mechanism having one member rotatable relative toanother member, in combination, a resilient pivot pin weakened to yieldto torsion and reinforced to resist bending stresses, said pivot pinhaving a portion rigidly secured to one of said members and anotherportion rigidly secured to another of said members, whereby said membersmay be rotated relative to each other a short angular distance aboutsaid pivot pin by torsion of said pivot pin, and means to compensate forthe resistance to torsion offered by said pivot pin, said meansincluding an over-center spring acting on said rotatable member.

4. The construction according to claim 3, where said over-center springconsists of a compression spring forming a toggle with said one memberwhere a portion of said one member acts as one leg of said toggle andsaid spring acts as the other leg of said toggle, said legs form ing anapproximately straight line pointing towards said pivot pin.

5. In a weighing mechanism including a double armed fulcrumed beam and astationary support, the arms of said beam being subjected togravitational forces acting at certain points, in combination, aresilient pivot pin to serve as fulcrum for said beam, said pivot pinbeing weakened to yield to torsion and reinforced to resist bendingstresses, said pivot pin having a portion rigidly secured to saidstationary support and another portion rigidly secured to said beamwhereby said beam may be rotated about said pivot pin a short angulardistance by torsion of said pivot pin, and means to compensate for theresistance to torsion offered by said pivot pin.

6. The construction according to claim 5, where said means to compensatefor the resistance to torsion consists of a geometry where said fulcrumis below a line projected between said points where said gravitationalforces act so that the resultant gravitational force acts on a pointslightly above the axis of said pivot pin.

7. In a weighing mechanism including a member rotatable relative toanother member, in combination a pivot comprising a straight fluted pinof resilient material having radial fins extending longitudinally andparallel with the axis of said pin so as to be weakened to yield totorsional stresses, said pin having a portion rigidly secured to one ofsaid members and a spaced portion rigidly secured to the other of saidmembers, an intermediate portion of said pin being unsupported to befree to twist about its axis, whereby said members may be rotatedrelative to each other a short angular distance about said pin bytorsion of said pin, said pin having an axial hole in said unsupportedportion to further weaken said pin against torsional stresses.

8. A weighing mechanism having a stationary mem ber comprising a pivotalsupport, a weighing beam carried by said pivotal support, said Weighingbeam having an arm extending horizontally from one side of said pivotalsupport to carry an adjustable weight, another arm extendinghorizontally from an opposite side to pivotally support a load carryingmember, said load carrying member comprising a platter to receive a loadto be weighed, a rack on said load carrying member to carry complementalweights, a rack on said stationary member to receive complementalweights removed from said rack, said complemental weights being of knownWeight, whereby said beam is in balance when said complemental weightsare carried by said rack of said load carrying member with no load onsaid platter, a fluted pivot pin of resilient material for said pivotalsupport, said pin having ends rigidly supported by said stationarymember and a central portion rigidly secured to said weighing beam, sothat said beam may be rotated a short distance by torsion of said pin,and means to compensate for the resistance to torsion of said pivot pinto adjust the sensitivity of said weighing mechanism.

References Cited in the file of this patent UNITED STATES PATENTS671,789 Borgeson Apr. 9, 1901 1,702,455 Trumpler Feb. 19, 1929 2,082,968Morris June 8, 1937 2,087,354 Mufily July 20, 1937 2,238,380 Almen Apr.15, 1941 2,417,392 Craig Mar. 11, 1947 2,681,222 Stelzer June 15, 1954

